Method and apparatus for electrolytic etching



l 1965 M. FEINER ETAL 3,208,923

METHOD AND APPARATUS FOR ELECTROLYTIC ETGHING Filed 0ct. 24, 1960 2 Sheets-Sheet 1 CONTROL CONSOLE O 0 O O GEN Is (D |7b I70 FlGfl- ELECTROLYTE m INVEN TOR. MELVIN FEINER SAMUEL YOUNG JR. BY CLAYTON C. SHEPHERD JR 1M & 777M ATTORNEY 23, 1.965 M. FEINER ETAL 3,208,923

METHOD AND APPARATUS FOR ELECTROLYTIC ETCHING Filed Oct. 24, 1960 2 Sheets-Sheet 2 CONTROL cousous o INVENTOR. MELVIN FEINER SAMUEL YOUNG JR BY CLAYTON C. SHEPHERD JR ATTORNEY relation to said workpiece.

' 3,208,923 METHOD AND APPARATUS FOR ELECTROLYTIC 1 ETCHING Melvin Feiner, Monterey Park, Clayton C. Shepherd, Jr., Bellflower, and Samuel Young, Jr., La Mirada, Califl, assignors to North American Aviation, Inc. Filed Oct. 24, 1960, Ser. No. 64,504

i 8 Claims. (Cl. 204-143) This invention relates to the electrolytic etching of metallic materials and more particularly relates to a "wet wick. type method and apparatus whereby controlled removal of metals may be readily effected by a combination of chemical etching and electrolytic dissolution.

The term wet wick as stated and applied herein should be understood to mean the saturation of a porous member with an etchant constituent and the subsequent abutment of a workpiece thereagainst.

iiThetrend' of modern missiles and aircrafts to higher speeds has required that such vehicles be constructed of very high strength metals capable of withstanding extreme environments. The fabrication and in particular the chemical etching or milling of such missile and aircraft components mustbe expeditiously accomplished while yet maintaining very close tolerance control there- -over. The problem of maintaining close tolerance control over the workpiece becomes even more acute when complex structures such as a honeycomb core are fabricated to the desired contours.

' The prior art has attempted to fulfill such desiderata with present-day fabrication techniques, however, in many instances such prior art apparatuses and methods have proved inadequate. Heretofore, it has been conventional in the chemical etching or milling art to immerse the workpiece in an etchant composition in an attempt to effect. the desired controlled contours. Also, many electrolytic etching techniques such as the Method for Electrolytic Etching as described in U.S. Patent No. 2,767,137 have been employed, however, suchprior art techniques have not completely solved many of the present-day fabrication problems.

The present invention provides for the selectively controlled electrochemical wet wick etching of a metallic workpiece wherein a porous means saturated with an electrolytic etchant constituent is positioned in abutting A receptacle means is positioned below said porous means to receive and permit said constituent to flow through a pump means utilized to I pump the constituent from said receptacle means to said porous means. A generator means is operatively connected to said porous means and said workpiece for selectivel-y passing an electric current therethrough thereby completing the electrolytic etching function.

An object of this invention is to provide for the expeditions and closely controlled removal of high strength type metals.

' Another object of this invention is to provide for the expeditious fabrication of high strength type metals wherein very close tolerance control is maintained thereover.

A further object of this invention is to provide for the expeditious electrolytic etching of complex type contoured metallic surfaces.

A still further object of this invention is to provide for the expeditious electrolytic etching of circular component surfaces.

A still further object of this invention is to provide a meth'od'of electrolytic etching whereby selectively controlled removal of high strength type metals is easily achieved.

United States Patent 3,208,923 Patented Sept. 28, 1965 mold type embodiment employing the novel concepts of this invention.

FIG. 2 is a partial top view taken on lines 2-2 of FIG. 1.

FIG. 3 is partial elevational view disclosing a second impressed mold type embodiment employing the novel concepts of this invention.

FIG. 4 is a view similar to FIG. 2 with the parts thereof impressed mold type emrearranged to provide a third bodiment of this invention.

FIG. 5 shows a modification of the porous mold member employed with the FIGS. 1, 2 and 4 embodiments.

'FIG. 6 isa schematic view disclosing afourth lathe type embodiment employing the novel concepts of this invention.

FIG. 7 is a cross-sectional view taken on line 7-7 of FIG. 6.

FIG. 8 is a cross-sectional view taken on line 8-8 of FIG. 6.

The purpose of this invention is to provide for the selectively controlled electro-chemical wet wick etching of a metallic workpiece wherein a porous means is initially positioned in abutting relation with the surface of the workpiece to be formed. The porous means functions to absorb and be saturated with an electrolytic etchant constituent to thereby wet and etch said surface.

In accordance with the hereinafter illustrated preferred workpiece for selectively passing an electrical currenttherethrough thereby completing the electrolytic etching function.

FIG. 1 and FIG. 2 disclose a ing the novel wet wick concepts of this invention and is particularly directed to an impressed stationary die type operation. A metallic workpiece 1 having a surface 2 thereof adapted to be selectively contoured is secured by any desired conventional means to an adapter plate 3. The workpiece 1 may comprise, for example, a relatively complex honeycomb type structure as shown. It is to be also understood that the surface 2 of workpiece 1 may comprise any desired initial configuration such as flat, round, etc. The workpiece 1 may further comprise any desired available high strength materials such as Ren 41, Vasco Jet 1,000, 15-7 MO Steel, titanium, etc. as well as relatively low strength type materials. Although the FIG. 1 and FIG. 2 embodiment and also the hereinafter described additional embodiments are particularly adapted for the fabrication of metallic materials, it is believed to be well within the spirit of this invention to use such embodiments for the production of non-metallic workpieces, for example, a plastic based material. It will reference works such as Air Weapons Materials Application Handbook, Metals and Alloys, ARDC TR 59-66,

first embodiment employ- I rate. of such an ,3 published by the US. Air 'Force published by the American Society for Metals.

A pulley wire 4 is connected at one end to the adapter and Metals Handbook plate 3 and at the other end thereof to a counterweight.

5 which functions to accurately control the impressed weight of the workpiece. The pulleywilre 4 is draped over a conventional type grooved pulley wheel 6 so as to effect the desired supporting function. It should be noted that the pressure imparted by the workpiece -1 may be readily governed by" other convenient support type methods. For example, shouldit be desirable to'impress the workpiece 1 with'a force greater than its own weight, weight members may be placed thereon to fulfill such a function.

' A porous mold member on porous means 7 comprises an upper contoured die surface 8 thereof juxtaposed to the lower surface 2 of the workpiece 1. As more clearly shown in FIG. 2' the upper surface 8 of the porous mold 1 member 7 is selectively contoured to the desired configuration comprising relatively high areas 8a and low areas 8b and is adapted to be'pressed against the surface 2 of the workpiece 1 so as to impart such a desired configuration thereto as shown by the dotted line 2a in FIG. 1. The porous mold member 7 may be formed of any desired'porous type material which is effective to permit the top and sides of the tube member 9. However,..it.

should be understood that the size and relative orientation of such holes are a matterof choice depending on the Y specific work assignment. The tube member 9 is extended the reception and controlled distribution of an electrolytic etchingconstituent therethrough to the upper surface 8 thereof (primarily due to the phenomena ofcapillary action). It isalso preferredto utilize a material which will maintain a relatively smooth and closely toleranced upper surface. 8. For example, the porous mold member 7 may comprise-aBO-lOO mesh sand type constituent, glass beads with diameters'of'1 mils, powdered graphite or a granulated plastic material. stituent is then mixed with 2-6% by weight of a binder which is also preferably inert 'with'respect to the etchant constituent. The size of the particles comprising 1 the porousmold-imember-7 is primarily determined by the type of electrolyticetching constituent employed therewith and in particular the rates at which his desired to flow such a constituent therethrough. The binder may be represented, for example, by the-following mixture:

- g Parts Epoxy resin; 80 Allyl glycidylether 20 Curative. Apco 320'(metaphenylene'diamine) 14 /2 The selected con- I at 11 to provide for an expeditious operative connection to a hereinafter disclosed fluidicircuit.

A receptacle means 15 is positioned below the lower surface'of the porous mold member 7 for receiving overflow of the electrolytic etching constituent therein. If desired, means 15 maycomprise a drain if it is not desired that the electrolytic etchant be circulated- A first transfer pipe 16, which comprises the first link in the fluid circuit,

is operatively connected to a conventional Vanton type pump 17 effective to discharge the electrolytic etchant constituent through a second transfer pipe 18 which is operatively connected to the extension portion 11 of'the metallic tube member 9. In the preferred embodiment the pump 17 has a constant discharge capacity of ap proximately 5 g.p.m. It is therefore necessary to provide means whereby the selective injection of theetchant'constituent may be regulated. For this purpose, a by-pass 'line 17a operatively connects discharge pump-17 and the receptacle 15. .A control valve 17b is constructed and arranged in the by-pass line to permit 'selectiveamoun'ts of-etchant constituent'therethrough With such an .al'r rangement it is apparent that the etchant constituent injected-into'the tube member 9 may be readily'controlled. A heater 19 is operatively connected to theqsecond transfer pipe 18 of the fluid circuit and may be selectively controlled to impart the desired amount of heat to the.

electrolytic etchant constituent. .A generator 20 isopcratively connected to a power'source and'is further operatively connected in series to the workpiece 1 (the anode and the extension portion 11 oftube 9 (thecathode) for The above epoxy 'resin used in the binder are glycidyl I polyether compounds of polyhydric alcohols and-poly hydric phenols of. the type described in U.S. Patents, No.

2,767,157, 2,921,040, andv 2,883,308. An example of such a polymeric. material is one obtained by the reaction of a mole of 2,2-bis(4-hydroxyphenyl)-propane with one or more mols of epichlo'rohydrinin the presenceof a base such as sodium hydroxide. This provides a glycidyl polyether composition having. terminal epoxy groups.

to distribute the electrolytic etchant constituent therethrough. Although only one such tube has been shown for illustration purposes it should be understood that any number thereof may be employed depending on the specific work application. Also, it may be'desired to oper-, atively .connect supplementary transfer. t'ubes laterally with respect to transfertube 9. As sho n in oth FIG- selectively. passing an electrical current therethrou gh.

It should be understood that if so desired the pump 17, heater 19. and generator 20 may be operatively connected to a control'console as shown for selective control so as tosubject the formed workpiece to a constituent;having the desiredpredetermined physical characteristics. It

should be further. understood that-if so desired, the impressed weight'of the workpiece may. also be selectively controlled by making the proper connections to the control console in a conventionalrnanner.

v embedded in the porous mold member 7 and is adapted The electrolytic etchant constituent utilized with the herein described embodiments may comprise any suitable electrolyte having the desired chemical etching properties, for .example, a constituent comprising 10 g. NaCl for every 95 cc. of water, 5. cc. of H PO -and .01% of Aerosol OT. Other examples-of electrolytic etchant constituents which may be utilizedin carrying forththe functions of the disclosed embodiments of this invention include any one of the following solutions alone or in combination: H SO HCl, HNO NaNO KNO KCL; each preferably plusa wetting agent such as Sorbit AC (sodium alkyl naphthalene sultonate), or Aerosol OT (anionic disulfosuccinate). It is to be understood that the predetermined selection of such an electrolytic etchant constituent primarily depends on the nature of the workpiece being etched.

METHOD OPERATION r predeterminedtemperature when subjected to. heater 19 abutting relation to the relatively stationary porous mold member provides for the expeditious fabrication of selectively contoured surface 2a.

It should be understood that the relative total downward displacement of the workpiece 1 with respect to the mold member 7 may be readily observed, by any convenional type indicating means, for example, indicia means vertically positioned on the exterior of the apparatus disclosed in FIG. 1 indicating the relative downward displacement of the workpiece with respect to the mold member. p

Example I The following procedural description is exemplary of the'novel aspects of this invention as particularly illustrated by the FIG. 1 and FIG. 2 embodiment.

Subsequent to the selective contouring of the surface, 8 of the porous member 7 by conventional mechanical milling methods an electrolytic etchant constituent comprising g. NaCl for every 95 cc. of water, 5 cc. of 85% H PO and .0l% of Aerosol wasajdded to the container 15. The turbo-pump 17 was actuated to discharge said constituent at a rate of approximately 5 g.p.m. The heater 7 functioned to heat said constituent to a temperaure of approximately 100 F. The current density was maintained by generator within the range of 0.5-1.5 (preferably 1.0) ampsper sq. in. at 10 volts.

The discharged constituent was then injected into transfer tube 9 and selectively distributed therefrom so as to saturate the porous member 7 and in particular, to completely and evenly wet the contoured surface 8 thereof.

Ahoneycomb'type workpiece 1 comprising a PHlS- 7MO steel was then selectively impressed against and advanced relative to the contoured surface 8 of mold member 7 for period of about 0.5 hour. The workpiece was chemically milled to a depth of approximately 0.5 in. thus, at a rate approximately 1.0 in. per hour. The workpiece was then removed and washed in a water bath.

The fabricated surface 2a of the workpiece was found to be substantially smooth and regular.

FIG. 3 discloses an alternative embodiment similar to that disclosed in FIG. 1 and FIG. 2 employing the novel impressed stationary die wet wick" concepts of this in 'vention. In this embodiment the workpiece 21 is positioned between the contoured die surface 22 of the porous mold member or porous means 23 and a plurality of strategically positioned constituent transfer pipes 24 having orifices 25 formed therein. The lower surface of the workpiece 21 is subsequently etched to the configuration noted by' the dotted profile line 21a, in conformance with contoured die surface 22. The transfer pipes 24 are preferably constructed of a metallic or plastic material which is not chemically affected by the etchant constituent. As shown, the etchant constituent spray patterns 26 emitted from orifices 25 function to assure a preselected even distribution of the constituent over the top surface of workpiece 2 1. In this embodiment the workpiece comprises a honeycomb type structure and therefore, the etchant constituent is free to flow down along the upstanding walls thereof onto the contoured die surface 22. Such a structural relationship assures an even distribution of the etchant constituent over the entire contoured die surface 22. Also, if so desired, the electrolytic etchant constituent could be sprayed onto the contoured die surface 22 prior to the placing of the workpiece 21 thereagainst.

FIG. 4 discloses another embodiment employing the novel concepts of this invention wherein the structural elements of FIG. 3 are rearranged so that the electrolytic etchant constituent is evenly sprayed on the top, noncontoured surface of the porous mold member or porous means 23. The etchant constituent is then free to soak through the mold and wet the bottom, contoured die surface 22. The spent etchant flows downwardly, along the walls of the workpiece 21 and into the container 15.

The alternative embodiments illustrated in FIGS. Sand 4 may readily employ the fiuid circuit 16, 17, 18 and 19 of the FIG. 1 embodiment. In such a case, the fluid circuit could be arranged to inject the etchant constituent into transfer pipe 24. The method of operation for the FIGS. 3 and 4 embodiments is substantially the same as the hereinbefore described method of operation of the FIG. 1 embodiment.

FIG. 5 discloses a porous mold member 27 which may be utilized in lieu of the molds of the FIGS. 1, 3 and 4 embodiments. The contoured surface 28 thereof is covered with a thin coating 29 comprising a relatively electrically insulative type material which has a predetermined desired porosity. Such a coating 29 may comprise, for example, silicon carbide, zirconia or alumina which materials can be readily bonded to the mold member 27 in a conventional manner. The porous member 27 comprises a highly conductive type molded material such as sintered steels, powdered graphite or powdered carbon. The porous member 27 and coating 29 preferably comprise a material not chemically affected by the etchant used therewith. The porous mold member 27 is adapted to be operatively connected to one terminal of the generator 20 during the electrolytic etching of a workpiece. During the utilization of the porous means of FIG. 5, the method set forth in Example I was substantially followed. The only difference therebetween is that a current density within the range of l0-20 amps per sq. in. was readily maintained. v

FIG. 6, FIG. 7 and FIG. 8 disclose another embodiment employing the novel wet wick" concepts of this invention and are particularly directed to the electrolytic etching of circular surface by means of a lathe type operation. In accordance with this particular embodiment a metallic workpiece 30 is supportingly adapted to be rotated and have the outer surface thereof etched to the desired circular cross-section depicted by the dotted line 30a. A conventional motor means 31 is operatively connected to the workpiece 30 by a conventional type coupling means secured to the rotatable shaft 32 thereof. The coupling means, as more clearly shown in FIG. 7, may conveniently comprise an adapter plate 33 secured to the rotatable shaft 32 by standard thread means 34. Adapter bolts 33a extend through said adapter plate into threaded engagement'with the workpiece 30, as

shown. With such an arrangement selective actuation of the motor means 31 effects a rotation of the workpiece 30. It should be noted that the thread means 34 must be formed in a direction opposite to the rotation of motor means 31 to thus assure a positive connection thereat during the entire operation.

A metallic tube member 35, similar in construction to the tube members of the hereinbefore disclosed embodiments, functions to receive an electrolytic etchant constituent therein. As more clearly shown in FIG. 8, a flexible wick member or porous means 36 projects through slot 37 formed in the upper wall portion of tube 35 and is adapted to absorb the electrolytic etchant constituent therein. The wick member 36 is preferably formed of any conventional type wick material such as asbestos or glass-wool which material is resistant to the acid type etchant constituents employed therewith and yet maintains the desired constituent absorbing characteristic. The flexibility and positioning of the wick member relative to the workpiece 30 should be such so as V I to subject the fabricated portions-of the workpiece to the desired distributions of the etchant constituents during the entire etching process.

Sincefthe reduction of the outside diameter of the workpiece 30 necessitates a constant lowering thereof with respect to therelatively stationary wick'rnember 34 a means is necessitated to expeditiously perform such a function. ,In accordance therewith and for illustration purposes a piston assembly 38 is disclosed in FIG. 6 and comprises a-piston member 39 slidably mounted in a stationary housing 40. As shown, apiston rod 41 is securely connected to both the piston member 39 and the motor means 31 so as to provide for ,the relative vertical movements of said motor means. An inlet line or tube 42 is operatively connected-to said stationary housing 40 and is adapted to selectively permit the passage of an operating fluid means therethrough, on the underside of the piston member 40 so as to selectively raise said motor means. An outlet line or tube43 is also operatively connected to said housing 40, on the top side of said piston member so as to selectively lower said motor means... With such a conventional type arrange, ment it is apparent that selective injection and drainage of' the fluid means transmitted through lines 42 and 43, respectively,conveniently permits the vertical adjustments of said motor m'eans by means of a conventional pump operatively connected to said tubes 42 and 43.

The fluid circuit utilized. to inject the electrolytic etchantconstituent into the tube member 35 is. essentially the" same as the one employed in the hereinbefore described embodiments. Sincethe workpiece 30'is rotated 8 Example I! To the container of theFIGS, 6-8 embodiment, a substantial amount of electrolytic etchant constituent.

comprising 3 parts concentrated (12 N)Hcl, 1 part con-. centrated HNO (15 N) and 1 part H O, was added.

The turbo-pump 17 was actuated to discharge said con-,

stituent at a rate of approximately 5 'g.p.m, The heater functioned to heat said constituent ton-temperature. of approximately 140 F. A current density of 80 amps per sq. in. was maintained by the generator 20 at 10 volts.

A solid workpiece 30, square in cross-section (one sq.

" in.) comprised a carbon steel (approximately .8% car- I bon). The workpiece was selectively rotated atabout 20 r.p.rn. and initially positioned with oneof the corners thereof in abuttingrelation withthe top dfiwick member V' 34 as more clearly shown in FIG. 8. .The' workpiece.

was then selectively lowered with respect to wiokmember 34 so as to constantly maintain the. juxtaposed surfaces, contact. Such an adjustment was readily .madej when it would appear to the eyeof the operator that sufficient.

. electrolytic vetchant'constituent was not being imparted with the wick member 34. The abovestated procedure I was followed for approximately 1.5 hours, until the workin this particularembodiment it may be considered advantageous to usea brush typecontact'44 connected to the positive terminal of the generator 20.

METHOD OF OPERATION When the wick member 36 becomes sufiicientlysatur rated with the-etchant-constituent, the pistonassembly is selectively actuated to lower the workpiece 30 relative to said wick member into the. contacting position shown in FIG. 8. The workpiece30 is then-selectively lowered into contact with the wick member to constantly maintain the completed circuit to thereby assure the desired electrolytic function and further assure constant progressive etchingof theworkpiece. i

The eye of a skilled operator can be utilized to readily determine when the workpiece 30 .should be lowered relative 'to the wick member 36. However, it should be understood thata signal means of the conventional type may beoperatively connected to the control console and the etching circuit comprising generator .20, workpiece 30 (the anode), the etchant constituent contained in wick member 36 and the'tube member 33 (the cathode) to warn the operator that the circuit has been broken. It should be further understood that the control piston means 38 may also be operatively connected to the control console and such an aforementioned-signal means in order to automatically maintain the desired workpie'ce wick member'contact. When the surface 30a is fabricated to the desired diameter, the finished product may then be expeditiously removed by means of the adapter bolts 33a. The desired diameter may be readily noted by means of a conventional micrometer, calipers or the like. V

to the etched contacting surface of the workpiece,-i.e., when the workpiece 30 appeared to be out of contact piece comprised the circular configuration noted by the doted line 30a of FIG. 6 and .FIG. 7 (approximately one inch in diameter). The workpiece was then. 1'6? moved and washed in a water bath. The fabricated surface 30a of theworkpiece was found to be substantially smooth and regular.

It should be understood FIGS. 68 embodiment may be readily employed to form internal as well asexternal circular. surfaces.

The hereinbefore describedporous meansncomprising.

the porous mold members of the FIG. 1, FIG. 3 and FIG. 4 embodiments and the wick .member 360i the. FIG. 6 embodiment should be constructed and arranged.

in the majority of fabricating procedures to 'assurethe following desired functions: adequate electrolytic etchant constituent flow rates providing for continuous and fresh constituents thus, minimizing lay-product buildup and excessive reaction heat; uniform solution distribution to insure uniform metal removal; chemical inertness with respectto the etchant constituent providing for dimensional stability of the porous means; abrasion resistance; withstanding of slight shocks encountered during handling and the like; producing sharp details on the, fabricated workpiece; and maintaining a cathode of sufiicient surface area so as to assure adequate current densities.

As hereinbefore statedflthe output of the pump 17,.

heater 19 and'generator 20 maybe selectively controlled and varied tovsubject the workpiece to the desired controlled constituent. Also, any desired electrolytic etchant constituent which will effect the desired controlled etch rate may be employed herein. The, optimum range of operating conditions for the above described'embodiments when etching steels such as 15 -7MO steel, Vasco 6o jet 1,000 andCres'steels (corrosion resistant steels) are as follows: electrolyte temperature, 160-l80 F.; voltage, 10-20 volts; current density,'50-l000 amps per sq. in.;

electrolyte flow rate, sufficient tov carry out gases. formed at both the anode and cathode. Such optimum operating conditions ordinarily provide. for etch rates. in the range of "1 0 20 mils per minute.

Although this invention has been described 'and'illustrated in detail, it isto be understood-that the same is by way of illustration and example only and is not to be .taken by way of limitation,'the spirit and scopeof this invention being limited only by the terms of the appended claims. We claim:

. 1.7A method for electrochemically-etching a surface of a workpiece comprising the steps of contacting a first.

-that, the above described 9 side of an apertured workpiece in abutting relation with a selectively contoured surface of a forming member, discharging an etching constituent onto a second side and through said apertured workpiece and electrochemically etching the first side of said workpiece in conformance with the contoured surface of said forming member.

2. The method of claim 1 further comprising the step of selectively impressing said workpiece onto said forming member with a predetermined amount of force.

3. A method as defined in claim 1 in which said forming member comprises a porous material and further comprising the step of passing at least a portion of said etching constituent through said porous material.

4. An apparatus for etching a pervious workpiece comprising: an electrically conductive porous mold member having an electrically insulative surface conforming to a desiredworkpiece surface; means for contacting the workpiece against the mold member; means for continuously passing an electrolyte through the workpiece and through said mold member; and-means for passing a current through the electrolyte between the workpiece and said mold member so that a surface of the workpiece v is electrolytically etched.

5. In an apparatus for shaping a pervious workpiece comprising: a porous mold member having a contoured surface conforming to a desired shape of the workpiece; -means for contacting the workpiece against said contoured surface of said mold member to form an assembly of workpiece and mold member; and means for passing an electric current between said contoured surface and said workpiece so that selected areas on said workpiece are etched; the improvement comprisingz'means on one side of the assembly for continuously flowing an electrolyte through said assembly and over said contoured surface.

6. The apparatus of claim wherein said contoured surface is of generally horizontal extent and said workpiece is above said mold member,

said means on one side of the assembly including electrolyte discharging means mounted above the assembly, whereby electrolyte willflow downwardly through the workpiece and mold member.

7. The apparatus of claim 5 wherein the contoured surface is of generally horizontal extent and said mold member is above the workpiece,

said means on one side of the assembly including electrolyte discharging means mounted above the assembly, whereby electrolyte will flow downwardly through the mold member and workpiece.

8. A method for electrochemically etching a surface of a pervious workpiece comprising the steps of contacting a first side of said pervious workpiece in abutting relation with raised portions of an electrically conductive first member having a selectively contoured insulative surface continuously flowing an electrolyte through both said first member and said pervious workpiece; and electrochemically etching the first side of said workpiece in areas in contact with said first member.

References Cited by the Examiner UNITED STATES PATENTS 607,484 7/98 Rieder 204-143 1,319,928 10/19 Kennedy -204-224 X 1,773,135 8/30 Flanzer 204-224 1,792,197 2/31 Stresau 204-24 1,844,928 2/32 Slepian 204-224 2,080,234 5/37 Schlotter 204-224 2,365,539 12/44 Flowers 204-143 2,463,711 3/49 Nagle 204-143 2,590,927 4/52 Brandt 204-143 2,833,702 5/58 Elfers 204-224 2,869,266 1/59 Hirdler 204-143 2,905,605 9/59 Keeleric et al. 204-143 2,934,631 4/60 Imalis et a1. 204-143 2,961,395 11/60 Icxi 204-224 2,967,813 1/61 Lindsay 204-143 3,002,907 10/61 Williams 204-239 3,048,528 8/62 Covington 204-141 FOREIGN PATENTS 335,003 9/30 Great Britain.

748,485 5/56 Great Britain.

WINSTON A. DOUGLAS, Primary Examiner. JOHN R. SPECK, JOHN H. MACK, Examiners. 

1. A METHOD FOR ELECTROCHEMICALLY ETCHING A SURFACE OF A WORKPIECE COMPRISING THE STEPS OF CONTACTING AT FIRST SIDE OF AN APETURED WORKPIECE IN ABUTTING RELATION WITH A SELECTIVELY CONTOURED SURFACE OF A FORMING MEMBER, DISCHARGING AN ETCHING CONSTITUENT ONTO A SECOND SIDE AND THROUGH SAID APETURED WORKPIECE AND ELECTROCHEMICALLY ETCHING THE FIRST SIDE OF SAID WORKPIECE IN CONFORMANCE WITH THE CONTOURED SURFACE OF SAID FORMING MEMBER.
 5. IN A APPARATUS FOR SHAPING A PERVIOUS WORKPIECE COMPRISING: A POROUS MOLD MEMBER HAVING A CONTOURED SURFACE CONFORMING TO A DESIRED SHAPE OF THW ORKPIECE; MEANS FOR CONTACTING THE WORKPIECE AGAINST SAID CONTOURED SURFACE OF SAID MOLD MEMBER TO FORM AN ASSEMBLY OF WORKPIECE AND MOLD MEMBER; AND MEANS FOR PASSING AN ELECTRIC CURRENT BETWEEN SAID CONTOURED SURFACE AND SAID WORKPIECE SO THAT SELECTED AREAS ON SAID WORKPIECE ARE ETCHED; THE IMPROVEMENT COMPRISING; MEANS ON ONE SIDE OF THE ASSEMBLY FOR CONTINUOUSLY FLOWING AN ELECTROLYTE THROUGH SAID ASSEMBLY AND OVER SAID CONTOURED SURFACE. 